Method of shaping a starch-bound



Unite Patented Sept. 22, 1959 METHOD OF SHAPING A STARCH-BOUND FIBROUS MASS Jack E. (iaston, Manheim Township, Lancaster County, Pa., assignor to Armstrong Cork Company, Lancaster, Pa., a corporation of Pennsylvania No Drawing. Application February 19, 1957 Serial No. 641,033

4 Claims. (Cl. 18--55) This invention relates to a method of flattening warped starchbound fibrous masses, and more particularly to a method of softening the starch binder to release stresses set up during the formation, drying, and subsequent processing of the fiberboard.

In the manufacture of sound-absorbing decorative materials for installation on ceilings and walls, and particularly the fire-resistant acoustical materials comprising mineral wool or other inorganic fibers bound with a starch binder, it has been found that during the drying process to remove the water used in initially forming the water-laid mass the exterior portions of the board dry more rapidly than the interior. As the interior of the board dries, it shrinks, placing the exterior surfaces under compression. In order to render these materials soundabsorbent, it is necessary to have sound-absorbing passages on the surface of the material exposed to the interior of the room in which it is installed. These soundabsorbing passages may be in the form of holes drilled through the surface into the interior or they may be in the form of irregularly shaped fissures. In forming the fissures, the newly formed wet mass is subjected to the pressure of a fissuring roll. This fissuring roll ruptures the fiber orientation beneath the surface and causes fissures between adjacent clumps or groups of fibers. After the board is dried and the above referred stresses have been set up on the two outside surfaces, any exposure of one surface to conditions differing from those to which the other surface is exposed unbalances the stress system and causes the tile to warp. In the case of the drilled acoustical material or dry fissured acoustical material, the cutting of a certain amount of the stressed fibers disposed on one surface without disrupting the other surface unbalances the stress system sufficiently to cause the board to warp. Also, the application of paint to the newly exposed surface for the purpose of decorating the same changes the surface characteristics to such an extent that it too aids in causing the fiberboard to warp.

Many different methods have been used to overcome this warpage, some of which have been the application of a wet coating to the rear surface of the board to place a stress on the fibers in the back of the board to attempt to balance the stress on the face; however, this requires considerable time and the degree of flattening obtained from this method is not sufficient to warrant the time required for effecting the same.

The warpage in many instances is so great that the tiles are not acceptable for installation on ceilings.

It has been found that if the tile is subjected to a limited treatment of steam so that the steam penetrates the tile from one side, condensing on the binder in the tile, this condensed moisture has a suflicient softening effect on the binder to permit the fibers to reorient themselves, releasing the stresses which have been set up during drying; and then immediately upon shutting off the steam, or removing the tile from its exposure to the steam, the starch binder will harden and the board conforms to the general contour of the support on which it is reposing at the time it is removed from its subjection to the steam treatment.

It should be borne in mind in carrying out this inven tion that while the tile in this softened condition will tend to sag and assume the general contour of the support on which it is placed, it will not conform to sharp angles and projections.

An object of this invention is to provide a method whereby water-laid masses made of inorganic fibers bound together with a starch binder may be effectively flattened after they have been dried by condensing steam in the board to soften the binder.

In carrying out this invention, it has been found that conventional mineral wool acoustical tile, such as that sold under the trademark Travertone, may be made in the regular manner, using the wet fissuring process and the conventional drying equipment after fissuring. The formed sheets are then sanded, painted, and cut into tile of the desired shape and size. During these operations, a certain amount of warpage occurs due to the unequal stresses from one side of the tile to the other. After this condition exists, it is impossible to balance the stresses. In order to correct this unbalanced stress condition, it has been found desirable to relieve the stresses so that the tile will assume a flat shape.

In carrying out the invention, the tile is placed on a conveyor belt which carries it to a steamimng station, where it is positioned over a steam chest. This operation can be accomplished at any stage in the manufacturing process but should, of coursre, be done after all other processing steps have been completed so that all the unbalanced stresses are present in the board at the time the treatment is effected.

It has been found desirable to place an open mesh cloth or other foraminous material over the steam chest to form a confining chamber for the steam; this enhances the introduction of steam into the bottom surface of the tile. The steam passing into the tile condenses and the moisture formed upon condensation softens the starch binder to the point that the stressed fibers can move in the binder to such an extent that they can reorient themselves to permit the title to assume the configuration of the flat steam table on which it has been placed. It has been found that for good operating conditions, the tile should be held at a temperature less than F. for approximately 15 seconds while exposed to the steam. The higher the temperature the less moisture will condense on the binder. Also, if very low temperature tile is treated, the steam may not penetrate into the tile for a suflicient depth but may condense close to the surface, thereby increasing the resistance to deep penetration. After this minimtnn application of steam, which is only for approximately 15 seconds, the tile is removed from the steam table; and upon removal from its exposure to the steam, flash evaporation of the moisture is effected and the binder hardens to the extent that it sets, holding the fibers firmly in their unstressed condition. The resulting tile is now free of internal stress and remains as flat as the surface on which it was positioned during this process.

The best method for carrying out this invention has been found to reside in the introduction of steam into one surface of the tile only. By this method, the steam passing through the tile forces the entrapped air ahead of it and discharges the air from the surface opposite that from which steam entered the tile. If this entrapped air were not permitted to escape, the steam would heat the air, which would in turn elevate the temperature of the tile to a degree where the amount of moisture which would condense on the starch binder would be insufiicient to soften the binder. This is a different aspect from merely subjecting a material which may be softened by the application of heat to a bath of steam which completely envelopes the material and introduces steam from all sides, attempting to get a uniform distribution of steam or other binder softening medium throughout the mass. If the tile were exposed to an envelope of steam so that steam is immediately available on all surfaces, the softening effect would not be suificient to accomplish the desired result at commercial operating speeds.

it will be obvious to those skilled in the art that l have developed a method of straightening starch-bound inorganic fiber masses by the simple application of steam for a very limited period to the zone of greatest stress. While the invention is described in connection with the use of steam, it Will be understood that any gaseous medium which would have a softening effect on the starch binder would be suitable for carrying out the invention and would have substantially the same results as the steam herein disclosed.

I claim:

1. In a method of flattening a dry starch-bound fibrous mass, the steps comprising placing the fibrous mass to be flattened on a flat foraminous surface, passing water vapor through the forarninous surface into one side only of the fibrous mass positioned thereon, said water vapor being at a temperature substantially greater than the temperature of the mass to condense the water vapor on the starch binder to soften the same, halting the passage of water vapor, and after the starch binder has rehardened removing the mass from the supporting surface.

2. In a method of shaping a dry starch-bound fibrous mass, the steps comprising placing the fibrous mass to be shaped on a foraminous surface of the contour desired for the fibrous mass, passing water vapor through the foraminous surface into one side only of the fibrous mass positioned thereon, said water vapor being at a temperature substantially greater than the temperature of the mass to condense the Water vapor on the starch binder to soften the same, after the mass, under the action of its own weight, conforms to the shape of the foraminous surface, halting the passage of water vapor, and after the starch binder has rehardened removing the mass from the foraminous surface.

3. In a method of flattening a dry starch-bound fibrous mass, the steps comprising moving the fibrous mass to be flattened on to a fiat foraminous surface, passing water vapor through the foraminous surface into one side only of the fibrous mass positioned thereon, said Water vapor being at'a temperature substantially greater than the temperature of the mass to condense the Water vapor on the starch binder to soften the same, and after the starch binder has softened removing the mass from its exposure to the Water vapor.

4. In a method of flattening a dry starchbound fibrous mass, the steps comprising placing the fibrous mass to be flattened on a flat foraminous surface, passing steam through the foraminous surface into one side only of the fibrous mass positioned thereon, said mass being at a temperature not in excess of F., halting the passage of steam, and after the starch binder has rehardened removing the mass from the supporting surface.

Powell May S, 1942. Courtright Mar. 14, 1950 

1. IN A METHOD OF FLATTENING A DRY STARCH-BOUND FIBROUS MASS, THE STEPS COMPRISING PLACING THE FIBROUS MASS TO BE FLATTENED ON A FLAT FORAMINOUS SURFACE, PASSING WATER VAPOR THROUGH THE FORAMINOUS SURFACE INTO ONE SIDE ONLY OF THE FIBROUS MASS POSITIONED THEREON, SAID WATER VAPOR BEING AT A TEMPERATURE SUBSTANTIALLY GREATER THAN THE TEMPERATURE OF THE MASS TO CONDENSE THE WATER VAPOR ON THE STARCH BINDER TO SOFTEN THE SAME, HALTING THE PASSAGE OF WATER VAPOR, AND AFTER THE STARCH BINDER HAS REHARDENED REMOVING THE MASS FROM THE SUPPORTING SURFACE. 